A significant week for English rugby is about to end with the most thunderous occasion of the Aviva Premiership season. The league's two frontrunning sides, Saracens and Harlequins, will jog out at Wembley in front of a world record crowd for a club fixture, a far cry from the pie-and-pint era at Southgate when the pitch often had to be checked in advance for dog turds. Nowadays you are more likely to trip over a member of a boy band – in this case McFly – or a cheerleader's pom-pom.

What the majority of onlookers really want to identify, though, is the likeliest winner of this year's title. Saracens, as defending champions, have a reputation as fast finishers and stuck 45 points on Sale away from home last week. They have also beaten their London rivals in their last five successive league meetings, including a 19-11 defeat at a sold-out Twickenham in late December. Quins are three points ahead at the top but have not always managed to recapture their unbeatable form of last autumn.

Saracens also have a confident air about them, even with their two specialist opensides, Andy Saull and Jacques Burger, out for the remainder of the season and Brad Barritt rested. The Quins' director of rugby, Conor O'Shea, though, refuses to accept his multi-coloured leaders are on the slide. "We're very comfortable with where we are," replies O'Shea coolly. "We're ready for huge challenges and we're ready to be written of by a lot of peoplef. That in itself will motivate us."

He scarcely needs to add that no one gave Quins a chance when they travelled to Toulouse in the Heineken Cup pool stages, having lost at home to the same opponents the previous weekend. That glorious 31-24 win showed O'Shea's young side what can be achieved with the correct attitude and the requisite ambition. With their England captain Chris Robshaw back, even a sudden injury crisis at hooker has not eroded that belief. "We're very confident with what we're trying to achieve – and will achieve – over the next couple of years with this group," confirms O'Shea. "We're a side with a lot of years left in us. It's hard to believe Joe Marler is still only 21, George Lowe is 22, Jordan Turner-Hall is 24.

"People, as I say, will write us off and think we've done nothing remotely decent this year. When Leicester and Saracens win it's: 'Oh, they really know how to grind out wins.' When you're us it's: 'Oh, they're lucky.' We'll use that. We've enough in the memory bank to say that on our day we play rugby that is very hard to contain. The game is about taking your chances. The way we play we will create them and if we get momentum we're a very difficult side to defend against."

Harder, faster pitches will also favour their style and there is sufficient physicality up front not to be intimidated. If O'Shea has done anything since taking over at the Stoop almost exactly two years ago it is to make Quins relentlessly hard opponents. "Chris Robshaw, Nick Easter, Mike Brown ... talk about competitors. That's what you need, guys who aren't willing to take second best. I could name a good few more. If they're talented as well, you've got a chance."

This is among the reasons, he believes, why England's fortunes are destined to improve steadily. The 41-year-old O'Shea was on the Rugby Football Union's head coach advisory panel and believes Stuart Lancaster will soon be unleashing some world-class talent. "It's one of the things that brought me back into club rugby. I knew from my previous role within the RFU what was coming through. You can see it now at every club. Before I left the union, the last thing I did was grant an academy licence to Exeter. Look at them now. I think there is massive, massive potential for this England team to grow. It's quite a dangerous time for other countries."

His current priority, though, is to knock Saracens down a notch or two. Saracens may be coached by Mark McCall, his old London Irish team-mate, but O'Shea is no less motivated. Having given his players some respite with a week of netball, handball and rock-climbing, he has changed Quins' training schedules, ordering more intense sessions to ensure the team are primed for the all-important final push. "It's all about peaking at the right time. I'm pretty confident we can do that. I remember going to a seminar given by Declan Kidney years ago. He talked about inches and showed us two instances, one in which Ireland won a grand slam and one where they missed out. The differential was nothing. One set are heroes, the other are villains. We just have to hope we have that little bit of luck."